Well, there are the long-known last resorts of using water purification tablets, boiling, diluted bleach, etc. But there’s a new kid on the block, growing in popularity over the last several years: the personal water filter.
I may be a bit behind the curve on this one, but I’ve only recently become aware of several types of portable, lightweight, hollow fiber membrane water filters that you can use to drink water directly from potentially unsafe ponds and streams. These filters, the best-known of which are the LifeStraw from Vestergaard and the Sawyer MINI from Sawyer, let you suck water through them directly from the questionable source and drink it. Last month, a reader inquired as to why they weren’t on my list of emergency supplies, and I decided to investigate.
I was pretty impressed by these devices, at least regarding use in the undisturbed wilderness. I know that putting one end of a cylinder into a pond with Cryptosporidium and Giardia (which are as bad as they sound), or MONSTER PARASITES THAT EAT YOUR BRAIN (they are probably out there somewhere), and sucking water through the cylinder and DRINKING IT might sound concerning. However, these hollow fiber filters are quite good at keeping out the bad stuff while letting the water in, and still allowing water to flow quickly enough that you can drink it in real time. Time Magazine gave LifeStraw their award for Best Invention of 2005. The LifeStraw and Sawyer filters use FDA-compliant materials and yield water that the companies report to meet US EPA drinking water standards and World Health Organization “highly protective” category standard of safe water. Hang on, though, we’ll look more closely at these health claims in a minute.
|Hollow fiber filter (from Sawyer website)|
They do have a finite lifespan of use, however, with LifeStraw filtering up to 264 gallons (that’s 1000 liters, so it really is a round number) and Sawyer Mini filtering up to 100,000 gallons. They also store indefinitely. For a while, LifeStraws were given a storage life of 5 years but this was later revised to indefinite.
Most importantly, what about health?
LifeStraw filters through 0.2 micron pores. (A micron, or micrometer, is one one-thousandth of a millimeter; the typical bacteria living inside your gut is about 2 microns long and about 0.5 micron wide.) LifeStraw claims that this yields good drinking water, EPA compliant, etc. Sawyer filters to 0.1 microns or 0.02 microns depending on the version. Sawyer states that the 0.1 micron filter takes out 99.99999% of bacteria and 99.9999% of protozoans (like Cryptosporidium and Giardia), but does not remove viruses due to their smaller size. Sawyer thus considers this filter safe for travel around the North American wilderness but not for third world countries, in which viruses like hepatitis A in the water supply is a big concern. (Human-infecting viruses do not persist in the wild; their presence in the water is typically from contamination with human waste/sewage.) They claim that the 0.02 micron filter takes out 99.9997% of viruses and that this exceeds EPA recommendations, although they point out that the 0.02 micron filter takes a longer time to pass water, and suggest that you use the 0.02 micron filter if you will go to a third world country. Unfortunately, the 0.02 micron Sawyer filter system does not appear to be available in the small portable size, and is much more expensive.
(But wait, LifeStraw makes a big deal about its filters with their 0.2 micron filtration being used in developing countries; they have been partnering with various charities to give free filters to people in various African countries, Haiti after the recent typhoon, etc.; so this contradiction is confusing.)
It’s worth noting that these pore size figures are not the average pore size, with some pores being smaller and some larger; they are absolute pore sizes, so no pore should be larger than the number given. One more important point is that these are physical filters; they don’t include resins or activated charcoal so they don’t take out chemicals or bad tastes like commercial kitchen water filters do (for example, Brita). So if you use these to drink from germ-laden disgusting water, you’ll ingest germ-free disgusting water. And remember, no filter can let you drink saltwater.
Ok, so what about health AFTER AN EARTHQUAKE?
Still, what concerns us most in this article is: what about health in a modern city after an earthquake? After all, it’s one thing to wander around in the Rocky Mountains drinking from beautiful streams, but what will our water supply look like after an earthquake has potentially compromised our water pipes? Well, I checked with emergency planners and water quality engineers at the San Francisco Public Utilities Commission, and I have disappointing (not to mention rather disturbing) news from Water Quality Division Engineering Manager Manouchehr Boozarpour. Normally, our potable water pipes carry potable water, and our sewage pipes contain sewage, and never the twain shall meet... unless both kinds of pipes crack during an earthquake, in which case cross contamination is likely. Yep, THAT’s what they mean when they say you need to purify tap water after an earthquake, and because the sewage potentially introduces viruses, which are not removed by the 0.2 and 0.1 micron portable filters, the water from your post-quake tap is likely to be more dangerous than the water in the mountain pond.
So, unfortunately, a LifeStraw or Sawyer individual filter tube does NOT offer sufficient protection to drink potentially contaminated tap water after an earthquake in a city. The options that I can see to decontaminate suspicious tap water are to either pack one of these small filter tubes in your portable emergency kit but to also have water purification tablets packed to treat the water before you suck it through the filter, or to purchase one of the larger systems that would be intended for home use in the aftermath of a major quake but would be more difficult to take with you if you had to leave. These kits consist either of Sawyer’s 0.02 micron filter that theoretically removes the viruses, but is slow and requires a large pumping mechanism; or a system that includes both a filter and a chemical water treatment step designed to inactive viruses like the Sweetwater purification system. Note that chemical purification alone does not guarantee killing of Cryptosporidium and Giardia. Boiling is great, but you can’t assume you’ll have the necessary heating source to do it, and flame is never a good idea around potential gas leaks.
|Purification systems that remove or inactivate viruses|
The Centers for Disease Control has a very useful and detailed document about emergency water purification that is worth reading. (Just don’t be surprised to see their comment that you should observe printed expiration dates on commercially bottled water, which contradicts the FDA’s advice about which I wrote last year that you can ignore those dates. Remember that the FDA is the agency charged with regulating safety of bottled water, so I am comfortable giving priority to their advice on the matter.) One of the links on that page takes you to another useful guide about relative effectiveness of different chemical purification methods.
Bottom line: I still advise keeping sufficient emergency water supplies handy so that you don’t have to purify tap water in the first place. Still, we can’t know that a more extended water shortage won’t develop (remember, the Red Cross is recommending TWO weeks of emergency supplies now), so having the ability to remove microorganisms including viruses may still come in handy if the local authorities tell you that you can drink the water if it's been boiled.
I had never realized how much we take our water faucet for granted!
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